The invention relates generally to conical spiral antennas and more particularly to methods for manufacturing an insulated conical spiral conductor pattern.
Conical spiral antennas have a number of desirable features. They are particularly useful wherever a small broad band circularly polarized directional microwave antenna is needed. Since they are lightweight, compact and potentially inexpensive, conical spiral antennas are well suited to mobile and aerospace applications. A synopsis of the operating characteristics of this class of antenna may be found in Rudge et al, The Handbook of Antenna Design, Chapter 7 (1982).
In the past, conical spiral antennas have been made by a number of differnt techniques including winding wire or narrow conductive tape on an insulating conical substrate. Whatever the technique, prior art fabrication has relied first on the provision of the conical substrate and then the definition of the spiral conductor pattern on the existing conical surface. Typically, a set of interleaved helical conductors are wound onto a conical form. The pitch of the helix is not constant, as screw threads are; as the cone tapers down, the distance between the conductors grows smaller as the logarithmic function. Applying the conductor pattern to the surface in accurate conformity to a logarithmic spiral is made more difficult by the curvature of the cone which, of course, increases toward its apex.
The spiral conical antenna has been known for many years. However, it has been difficult to make and its electromagnetic properties have for the most part defied calculation. These two problems combine to frustrate optimization. What is needed is a fast, simple way to fabricate models of conical spiral antennas so that the optimum physical parameters of the antenna can be experimentally verified through trials on a number of candidate models.